The wireless portable internet system is a next generation communication system providing further mobility to short-distance data communication using a stationary access point in a like manner of a wireless local area network (LAN). One of various international standards for the wireless portable internet system has been suggested by the IEEE 802.16e working group. The IEEE 802.16, which is the standards for the metropolitan area network (MAN), represents a data communication network for the intermediate area between the local area network (LAN) and the wide area network (WAN).
To safely provide services, the IEEE 802.16 wireless MAN system has defined an encryption function for traffic data which has become an essential requirement for stability of services and networks.
To encrypt the traffic data, the IEEE 802.16 wireless MAN system has defined a method for generating a traffic encryption key and distributing one. To maintain the security of the traffic encryption key, the wireless MAN system has established a scheme for updating and distributing the traffic encryption key per a predetermined time. A subscriber station and a base station accordingly share the same traffic encryption key.
To perform an authentication function and a security function, the subscriber station and the base station use a Privacy Key Management Request (PKM-REQ) message and a Privacy Key Management Response (PKM-RSP) message. The subscriber station transmits a Key Request message included in the PKM-REQ message to the base station to request an allocation of a new traffic encryption key or an update of a traffic encryption key. The base station receives the Key Request message from the subscriber station, transmits a Key Reply message included in the PKM-RSP message to the subscriber station when the request of a new traffic encryption key from the subscriber station is appropriate, and transmits a Key Reject message or an Auth Invalid message to the subscriber station when the request from subscriber station is inappropriate. The wireless MAN system uses the traffic encryption key shared between both the subscriber station and the base station to encrypt or decrypt traffic data in the radio channel and to transmit or receive the encrypted or decrypted traffic data.
In addition, a method for updating a traffic encryption key for the multicast service or the broadcast service in the IEEE 802.16 wireless MAN system corresponds to the above-described method for updating the traffic encryption key for the unicast service. In detail, all subscriber stations request to update a traffic encryption key from the base station, the base station individually provides the same updated traffic encryption key to all requesting subscriber stations. If the traffic encryption key update procedure for the multicast service or the broadcast service uses the same procedure defined for the unicast service, then the system's loads caused by occupying the radio channel are substantially increased, and the radio resources are unnecessarily wasted. Therefore, it is needed to provide a new method for efficiently reducing the undesired usage of radio resources caused by the above-noted traffic encryption key update process.